Articles you may be interested inTemperature-dependent electroluminescence spectra of poly(phenylene-vinylene) derivatives-based polymer light-emitting diodes J. Appl. Phys. 97, 034505 (2005); 10.1063/1.1845580Determination of traps in poly(p-phenylene vinylene) light emitting diodes by charge-based deep level transient spectroscopy Using temperature dependent impedance spectroscopy in a broad frequency range (10 Ϫ1 -10 7 Hz͒, we have found that the ac behavior of indium-tin oxide ͑ITO͒/poly-͑p-phenylene-vinylene͒ ͑PPV͒/aluminum light-emitting diodes shows several features which cannot be described by the usual simple double RC circuit representing a depleted junction region and an undepleted bulk. Instead, our measurements in combination with a theoretical modeling suggest that the PPV bulk is composed of a highly doped region at the ITO interface and a region with lower doping at a higher distance to the ITO. Moreover, the boundary between these two regions is not sharp but there is a gradual change in dopant concentration. The large frequency range allowed us to identify two distinct processes corresponding to the PPV bulk and a third one to the junction. The bulk relaxation frequencies correspond to the characteristic dielectric relaxation frequencies of charge carriers in the high and low conducting sublayers and are proportional to the respective conductivities. The magnitude and activation energy of the relaxation time correlates well with results obtained from temperature dependent DC conductivity measurements. For ITO substrates we obtain activation energies of 0.4 eV and room temperature conductivity of about 10 Ϫ7 and 10 Ϫ9 S/cm for the high and low conducting sublayers, respectively. On gold substrates only one bulk process and no junction process with an activation energy of about 0.6 eV and a corresponding conductivity of 3ϫ10 Ϫ11 S/cm at room temperature is observed. The Schottky junction has been studied by temperature dependent capacitance-voltage spectroscopy at a low frequency of 0.16 Hz. The obtained acceptor dopant concentration from 1/C 2 plots varies from 1.4ϫ10 17 at room temperature to 6.9ϫ10 16 cm Ϫ3 at 200 K. Assuming a density of states between 5ϫ10 20 and 5ϫ10 21 cm Ϫ3 for the valence band the temperature dependent acceptor dopant density can be described with an acceptor ionization energy between 0.16 and 0.2 eV.

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The transport properties of ''interface-engineered'' edge-type YBa 2 Cu 3 O 7 Josephson junctions are investigated in detail. We have investigated the dependence of the current-voltage characteristics on external magnetic field, temperature, and microwave irradiation and compare them to the resistively shunted junction model. The temperature dependence of the critical current and the normal resistance allows us to draw conclusions to the transport of quasiparticles and Cooper pairs in the investigated ''interface-engineered'' junctions. We have studied the properties of junctions for which La doped YBa 2 Cu 3 O 7 is used for the superconducting electrodes. We will propose a model for the undoped and the La doped case which takes into account a barrier which consists of a series connection of a normal conducting layer and an insulator, containing superconducting microconstrictions.